SQL Server中的一个奇怪的操作问题:-100/-100 * 10 = 0 [英] A strange operation problem in SQL Server: -100/-100*10 = 0

问题描述

• 如果执行SELECT -100/-100*10，则结果为0.
• 如果执行SELECT (-100/-100)*10，则结果为10.
• 如果执行SELECT -100/(-100*10)，则结果为0.
• 如果执行SELECT 100/100*10，则结果为10.

• If you execute SELECT -100/-100*10 the result is 0.
• If you execute SELECT (-100/-100)*10 the result is 10.
• If you execute SELECT -100/(-100*10) the result is 0.
• If you execute SELECT 100/100*10 the result is 10.

BOL 状态:

当表达式中的两个运算符具有相同的运算符优先级时，将根据它们在表达式中的位置从左到右进行求值.

When two operators in an expression have the same operator precedence level, they are evaluated left to right based on their position in the expression.

还有

Level   Operators
  1     ~ (Bitwise NOT)
  2     * (Multiplication), / (Division), % (Modulus)
  3     + (Positive), - (Negative), + (Addition), + (Concatenation), - (Subtraction), & (Bitwise AND), ^ (Bitwise Exclusive OR), | (Bitwise OR)

BOL是错了，还是我错过了什么?似乎-放弃了(预期的)优先级.

Is BOL wrong, or am I missing something? It seems the - is throwing the (expected) precedence off.

推荐答案

根据优先级表，此是预期的行为.优先级较高的运算符(/和*)在优先级较低的运算符(一元-)之前进行评估.因此:

According to the precedence table, this is the expected behavior. The operator with higher precedence (/ and *) is evaluated before operator with lower precedence (unary -). So this:

-100 / -100 * 10

被评估为:

-(100 / -(100 * 10))

请注意，此行为与大多数编程语言不同，在大多数编程语言中，一元求反的优先级高于乘法和除法，例如 VB ， JavaScript .

Note that this behavior is different from most programming languages where unary negation has higher precedence than multiplication and division e.g. VB, JavaScript.

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